Composite solid propellants are generally formed by dispersing a solid particulate oxidizing agent in a crosslinkable polymeric binder. In addition to the oxidizing agent, it is conventional also to include various metallic fuel materials such as aluminum, boron or magnesium, for example, as well as high energy materials such as metal hydrides or explosives such as HMX and RDX, for example. In addition, when high burning rates are required, small amounts of combustion catalysts, particularly compounds of iron, chromium, copper and the transition elements such as: iron oxide; organoiron compounds such as ferrocene, mononuclear alkylferrocenes, and polynuclear ferrocene derivatives such as Hycat.RTM. and Catocene (available from Arapahoe Chemical Corp.); copper chromite; ferric ferrocyanide; and ferrous ferricyanide, to mention only a few of the well-known combustion catalysts; are added. After the particulate materials are thoroughly dispersed through the polymeric material, it is necessary to add a curing agent for the polymer to the mix to thoroughly distribute the same throughout the mass and then to cast the propellant into a suitable configuration. In this process, it is essential that adequate time be available in order to thoroughly disperse the curing agent throughout the polymeric mass and then cast the same before the viscosity of the mixture increases to the point at which it is no longer possible for the propellant mass to flow into the mold. A requirement therefore exists for a certain minimum pot life in most propellant casting operations during which the propellant containing the crosslinking agent must remain in a sufficiently fluid state. We have observed that propellant compositions containing the aforementioned combustion catalysts tend to have a substantially shorter pot life than similar compositions without these combustion catalysts and that, in many cases, these shorter pot lives effectively prevent the formulation of certain desirable compositions. We have also found that the undesirably low pot lives can be extended if the combustion catalysts are treated to remove therefrom certain trace impurities of ionic metals. It appears that these trace impurities of ionic metals are distinguished from the bulk of the metal content of the combustion catalyst by being present in a form which is soluble in the propellant binder. Therefore, the ionic metal impurities, hereinafter designated as "labile" metal ions, act as cure catalysts for the cure reaction of the propellant and are responsible for the undesirably short pot lives observed. When the treated combustion catalysts are used in the solid propellant formulations, the pot lives are extended to times approaching those observed when no combustion catalyst is employed, and there is no noticeable difference in the activity of the catalyst as a modifier of the combustion rate of the propellant.
It is accordingly an object of this invention to provide a method for treating combustion catalysts which removes therefrom trace labile ionic metal impurities.
It is another object of this invention to extend the pot life of solid propellant compositions containing combustion catalysts.
It is another object of this invention to provide a propellant composition containing a purified combustion catalyst.
These and other objects of this invention will be readily apparent from the following description.